External hard drive not working

all my files are intact and still play but they won't export. this message showed up when I plugged my hard drive in
"You can still open or copy files on the disk, but you can’t save changes to files on the disk. Back up the disk and reformat it as soon as you can."

i have a mac also

 

I sounds like the files have been set as ,,Read Only"

 

ty! i ordered a new external hard drive to back up the files to so i'll fix my current one when the new one arrives